This invention relates to marine seismic exploration, and more particularly, relates to determining the position of a towed marine seismic source.
In marine seismic exploration, impulsive sources, which are typically air guns, are suspended at some preselected depth beneath a float. The float is towed by an exploration vessel and there may be a plurality of such floats towed behind the exploration vessel. The exploration vessel may also tow a streamer cable to detect energy propagating upwardly from subsurface strata lying beneath the body of water in which the vessel operates.
The exploration vessel may determine its location in the body of water through the use of conventional navigation systems. Such systems determine the vessel's location but do not determine the location of any float(s), having impulsive sources attached thereto, that may be towed at varying positions and distances by the vessel. Early attempts to locate floats with respect to the vessel by employing the radar of the vessel and mounting radar reflectors on the float have not proven to be sufficiently accurate nor reliable. Similarly, attempts to use acoustic location devices have had the same or similar shortcomings.
These and other limitations and disadvantages are overcome by the present invention, however, and improved methods and apparatus are provided for locating towed floats relative to the towing vessel.